Aerosol radiative forcings induced by substantial changes in anthropogenic emissions in China from 2008 to 2016

Liu, Mingxu; Matsui, Hitoshi

doi:https://doi.org/10.5194/acp-21-5965-2021

Articles | Volume 21, issue 8

https://doi.org/10.5194/acp-21-5965-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-5965-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 8

Research article

|

21 Apr 2021

Research article |

| 21 Apr 2021

Aerosol radiative forcings induced by substantial changes in anthropogenic emissions in China from 2008 to 2016

Mingxu Liu and Hitoshi Matsui

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Final revised paper (published on 21 Apr 2021)
Supplement to the final revised paper
Preprint (discussion started on 13 Jul 2020)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review of Liu et al. acp-2020-520', Anonymous Referee #1, 03 Sep 2020
- AC1: 'Response to Referee #1', Mingxu Liu, 27 Oct 2020
RC2: 'Review of manuscript acp-2020-520', Anonymous Referee #2, 22 Sep 2020
- AC2: 'Response to Referee #2', Mingxu Liu, 27 Oct 2020
EC1: 'review of anonymous referee #2', Andrea Pozzer, 23 Sep 2020
- AC3: 'Response to Editor', Mingxu Liu, 27 Oct 2020

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Mingxu Liu on behalf of the Authors (27 Oct 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 Oct 2020) by Andrea Pozzer

RR by Anonymous Referee #1 (28 Nov 2020)

Suggestions for revision or reasons for rejection

The authors have addressed most of my previous comments. Some concerns remain:

1) Regarding my comment on the CRF estimates, there is no detailed description on how the scaling to AR5 forcing is done and, more importantly, what the justification is. I don’t think the CRF estimated from the simulations in this study can be scaled to the AR5 forcing for the following reasons:

• The AR5 effective radiative forcing is estimated for the global present-day condition, compared to the preindustrial condition, which is different from the contrast between 2008 and 2016 with emission changes only in East Asia.

• I also had a comment about the difference in methodology for cloud forcing estimate between this study (using the Ghan method) and the AR5. The cloud radiative forcings are incomparable even just for East Asia.

• On the other hand, if the emission reductions in China during 2013-2017 had a significant impact on the estimated CRF over East Asia, which was NOT included in the AR5 forcing estimates, how can the AR5 forcing be relevant to the East Asia CRF in this study?

2) The aerosol radiative forcing is largely determined by column AOD and the vertical distributions. Fig. S5 shows that the CAM5 AOD in East Asia and over the North Pacific is lower than both MISR and MODIS observations. The model also has a large bias in simulating the BC profiles (Fig. S1). Please clarify how this would affect the estimated BC direct forcing. How about the sulfate profiles?

3) Please include the information of simulations in the caption of Fig. 1. It appears that the surface sulfate and BC concentrations are unchanged between 2008 and 2016 over regions other than East Asia. This can be very misleading. The other regions probably should be masked out if their emissions are fixed at 2008. Emissions in the surrounding regions, especially in South Asia, has been increasing from 2008 to 2016. As also shown in the MISR and MODIS observations (Fig. S4), AOD in South Asia had a significant increase from 2008 to 2016. The non-local emissions can have an impact on aerosols in East Asia. This raises a concern about the estimated forcing in East Asia.

4) Line 306-319: As brought up previously, I don’t think it’s ok to provide the forcing trends based on results from two individual years. The emission reductions started from 2013. There is no physical basis to suggest the linear forcing trends. The estimated trends should be removed or changed to forcing difference instead.

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RR by Anonymous Referee #2 (30 Nov 2020)

RR by Anonymous Referee #3 (21 Dec 2020)

Suggestions for revision or reasons for rejection

In this work, the authors simulate the radiative effect of the reduction in Chinese aerosol emissions over the 2008-2016 period. They show that the reduction in aerosol emissions produced a significant reduction in the aerosol burden and radiative forcing. The combination of the SO2 and black carbon emissions reductions produces a larger effect that the effects of the individual components due to interactions between them.

The paper demonstrates some interesting effects, particularly the interaction between different aerosol components in an internally mixed aerosol scheme. Unfortunately, some of the method for calculating radiative forcing values (particularly the cloud component) is unclear, which makes interpretation of some of the results difficult.

(I have been asked to comment primarily on the radiative forcing aspects).

Major points

The scaling to the AR5 mean value is unclear - I assume it means that the ERFaci forcing pattern in the model (for the 2008 simulation) is scaled such that the global mean is -0.5 Wm-2. This means that the same scaling factor is applied everywhere? This should be explained clearly as it is important for the interpretation of the results.

I am not convinced that this scaling to the AR5 value for the ERFaci is appropriate. The spatial pattern of the ERF and particularly the cloud component varies significantly between models (e.g. Zelinka et al, JGR, 2014) and between the RFaci and adjustments (e.g. Gryspeerdt et al, ACP, 2020). This means that the ratio of the forcing in the study region to the global mean varies between models and processes. The AR5 estimate is based primarily on observation-based estimates, which themselves have been suggested to underestimate the ERFaci in recent reviews (e.g. Bellouin et al, Rev. Geophys, 2020).

Given it is not clear why the global mean ERFaci is over/underestimated in this work (and it doesn't appear to be stated anywhere), it is not clear that a scaling derived at a global level is applicable to forcings calculated only over China and the north Pacific. Are both 2008 and 2016 simulations scaled to the AR5 value? As mentioned by another reviewer, if the effect of these emission reductions is significant, this creates a further pattern effect which impacts the scaling performed.

It might be more appropriate to quote the model values (unscaled) and note that the model over/underestimates the global ERFaci. Where the forcing values need to be compared to the AR5 forcings/a measured value, this difference/scaling factor could be noted.

Specific points

L112 - The contribution on meteorology vs aerosol changes is a potentially important one. Given the simulated change in AOD is smaller than observed when using the nudged simulation, is the observed AOD change reproduced when comparing the new 2016 simulations the authors have done?

L148 - HIAPER Pole-to-pole

L171 - 'The variation' - in this and other locations, I think 'variation' is used to mean 'change'. Is that the case?

L230 - This would be a great opportunity to show if the 2016-meteorology simulations match the observations better than the 2008-meteorology simulations

L273 - contribute less

L306 - annual-mean

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ED: Reconsider after major revisions (05 Jan 2021) by Andrea Pozzer

AR by Mingxu Liu on behalf of the Authors (10 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 Feb 2021) by Andrea Pozzer

RR by Anonymous Referee #1 (28 Feb 2021)

ED: Publish as is (10 Mar 2021) by Andrea Pozzer

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Short summary

By integrating an advanced global climate model with the latest anthropogenic emission inventory, we quantify the aerosol perturbations to regional radiative budgets due to the changes in anthropogenic emissions in China from 2008–2016. We find that aerosol–radiation interactions lead to a relatively small net radiative forcing at the top of the atmosphere but contribute largely to surface brightening in China over the past few decades.